Consider the following sentences:
Stress-related sick leave is related to organizational complexity in important ways (Smith 1999).
Smith's study (1999) indicated that there are important connections between organizational complexity and stress-related sick leave.
The reference refers to the same text in both cases, but notice that it does very different work. In the second sentence, we are merely refering to the object (Smith's paper) that we are describing; we are making a claim only about what Smith said, not what is true in the world. We can go on to criticize Smith's study if we choose. In the first sentence, by contrast, we are citing Smith's study as support for a claim about the world that we want the reader to accept. We are implicitly saying that Smith was right. We are saying that we believe him and that we think the reader should believe him too.
Notice how this can be gleaned from the grammar of the sentence. In the first sentence the reference cites support for a whole sentence, a statement of fact. In the second sentence the reference only guides our interpretation of the words "Smith's study".
I raise this because I sometimes get the sense that authors use references as in the first sentence when they only really intend the meaning of the second. That is, when pressed about the truth of the claim they will say, "Well, that's what Smith said." It's important here not to give referencing the magical power to turn anything that has been written down into truth. Some studies (especially meta-studies) do allow you to support statements of fact. Others you really only want to use as part of a larger argument for that fact.